In modules of ball grid array (BGA) type, an inter-board connection structure that electrically connects electrode pads between boards by using solder bumps is adopted.
In a conventional inter-board connection structure, in order to reduce a parasitic capacitance component formed between a pad on a dielectric board, and a ground conductor located in an inner layer of the dielectric board, thereby improving the high frequency characteristics, a part of the ground conductor which is directly under the pad is removed to form a punched hole. However, because a punched hole of the ground conductor causes coupling with a wire located in the inner layer of the dielectric board, there is a case in which such a punched hole cannot be used for an inter-board connection structure.
For example, in Patent Literature 1, a structure for improving the high frequency characteristics without making punched holes of a ground conductor is described. In a structure described in Patent Literature 1 for connecting a substrate and a semiconductor element, the length of a plated stub and the shape of an external electrode pad are set in such a way that, in the substrate, the plated stub and the external electrode pad exhibit capacitivity within a desired frequency range.
Further, by limiting a conductor wire extending from the external electrode pad to a part connected to an electrode pad of the semiconductor element to within a range within which the electrical influence of the plated stub or the external electrode pad reaches, a line having uniform impedance is implemented.